Wood laminate bonded with an adhesive comprising melamine formaldehyde resin and an ester of glycerol and sebacic acid



Patented Feb. 19, 1952 UNITED STATE S PATENT OFFICE WOOD LAMINATE BONDEDWITH AN ADHE- SIVE COMPRISING MELAMINE FORMAL- DEHYDE RESIN AND AN ESTEROF GLYC- EROL AND SEBACIC ACID John C. Mead and William C. Schneider,Stamford, Conn., assignors to American Cyanamid Company, New York, N.Y., a corporation of Maine No Drawing. Application September 7, 1946,Serial No. 695,548

Claims.

other object of this invention is to provide a relatively short andflexible set-up and pressing time for bonded articles having anincreased glue line strength. A further object of this invention is toprovide an adhesive suitable for radio frequency gluing techniques whichwill have an excellent working life. Still further objects of thisinvention is to provide a process for preparing an adhesive suitable forradio frequency gluing, requiring a minimum power consumption andproducts bonded therewith.

The foregoing and other objects and advantages of this invention areobtained by incorporating a relatively small amount of partiallyesterified sebacic acid glycerol into a dry thermosetting aminotriazineresin, or solution, dispersion, and emulsion thereof.

In order to more adequately and fully describe this invention, thefollowing examples are given by way of illustration.

EXAMPLE 1 Partially esterified sebacic glycerol was prepared bymixing202 parts of sebacic acid and 92 parts of glycerol into a paste andheating on a hot plate. Melting began in 5 minutes, at the end of whichtime the temperature had risen to 215 C. A clear amber which upon codingformed a cream-colored soaplike solid.

EXAMPLE 2 esterified sebacic acid glycerol prepared according to Example1 to give compositions containing up to sebacic acid glycerol. These drycompositions were then dispersed in water to form suspensions containing50-60% solids. The gluing suspension prepared in this manner was liquidwas obtained,

spread on 1 birch panels (4" x 12") using 8 grams of glue per panel.After setting overnight, these panels were assembled in three ply andpressed in a radio frequency press at 250 p. s. i. The total pressingtime was 8 minutes with radio frequency of 4.2 kw. input applied onlyduring the first few minutes. The following table summarizes the resultsobtained with these compositions:

Dry Soak 48 Hours Boil 3 Hours sexbagic cl Glycerol lbs. w s lbs. F$$lbs. Wig

Break Failure Break Failure l Break Failure Per cent 350 260 100 260 100l 430 340 100 350 100 l 400 100 370 100 390 100 l 440 360 450 100 3 430I00 310 100 300 100 5 480 90 300 50 280 100 10 360 60 240 100 220 100 1Delaminated.

The A. S. T. M. pamphlet entitled "A. S. T. M. Standard on Adhesives,dated January 1950, page 819, defines wood failure as The rupturing ofwood fibers in strength tests on bonded specimens, usually expressed asthe percentage of the total area involved which shows such failure. TheU. S. Department of Commerce pamphlet numbered 6845-45, entitledPlywood; Douglas Fir, dated January 27, 1945, sets forth on pages 5 and6 a lengthy discussion of tests to be applied to bonded wood panels, andtherein is set forth a discussion of wood failure and minimumrequirements thereof.

Adhesive compositions were prepared according to procedure of Example 1using 0.25%,

0.5% and 1.0% partially esterified sebacic acid glycerol. Thesecompositions were tested with a working life of 7 hours and an overnightset. The 0.25% composition was a syrupy paste, the 0.5% composition wasa thin paste whereas the 1.0% composition was a soft paste which wassatisfactory to meet the requirements of a good adhesive. Accordingly, acomposition containing 1% partially esterified sebacic acid glycerol wasprepared according to Example 1, and several other factors were variedto determine their effect on the ultimate glue line strength.

EXAMPLE 3 Birch panels of the type described in Example 1 were coatedaccording to the procedure there described with an aqueous dispersion ofa melamine formaldehyde resin containing 1% partially esterified sebacicacid glycerol. In the lamination of these panels several factors werevaried to determine the effect on the ultimate curing and glue linestrength. For example, the set up time was varied at 1 hours, 3 hoursand 5 hours; the radio frequency exposure time was 3 varied at 1 minute,1% minutes and 2 minutes, and the pressing time was varied at 2, 3, 5, 6and 8 minutes. One minute radirfrequency exposure time was found to beinsufllcient for cure. Accordingly, the following tabulation of resultspoint of the final acidity of the fixed glue, the lower acid number ispreferable. It was found that a composition containing 2 parts sebacicacid glycerol-Solox" solution mixed with 100 parts 5 melamineformaldehyde in aqueous suspension is compiled from only the 1 and 2minute radio gave an adhesive causing a relatively large temfrequencyexposures. perature gradient between the glue line and the Dry Soak 48Hours Boil 3 Bra. om u 1 11 on one me Minutes lbs. gfgglbs. a 'lbs. g g-Em Failure Break Failure Break Fal re .8 U a so a s3 is 2 400 0 s90 so530 mil a 550 so 530 100 400 100 z a .02. e2 .03 as .03 a see 100 490100 440 100 a 580 100 no 100 480 100 am. Set Up:

s 310 10 430 400 so 2 Min. R. F 5 560 100 480 so 410 100 l a e20 100 s1090 590 so a 530 100 460 100 420 100 134 Min. as. s 600 so 310 100 390100 a 630 so 620 100 540 100 5 hr. Set Up:

s e00 100 590 100 e10 100 6 e20 100 540 100 430 100 2 Min. a. 1-2. a see100 550 100 440 )0 3 e 100 550 100 also 100 2 650 so 580 100 580 100 s700 100 145 100 580 so 0 e l00 550 we 590 100 l)5Mln.R.F a 590 o 520 100310 100 a e 100 530 100 410 100 2 660 100 510 so 450 100 In all of theabove experiments there was no wood when in the radio frequency field.This explosion or wood charring during the laminatas is a very desirableaction.

The following examples illustrate the utility of The working life 0! thepartially esterlfled sebacic acid glycerol in a 50% Solox solutionsebacic acid glycerol melamine formaldehyde adas an accelerator foraminotriazine aldehyde ad hesive was found to be approximately 24 hours,hesives. and panels coated therewith were sumciently dry (0 EXAMPLE 4after 1 /2 hours for use in lamination. With thin 100 parts of drypowdered melamine formaldesections 01 laminae. a Short a Cycle a /2 hyderesin prepared according to the procedure i788 radio freq n y time. and2 minutes Press of Example 1 were dispersed in 65 parts of water. timeat 250 p. s. i. is more than satisfactory. to which there was added 2parts of a 50% o d y. complete fabrication can be accom- "Solox"solution of partially esterlfied sebacic Dlished, if necessary. n s than2 hours f m acid glycerol prepared according to the procedure e t OfSpreading glue fidhesivewith this of Example 1. This Solox" solution ofsebacic adhesive, set up time and press time are very acid glycerol hadbeen reacted to an acid numfiexible and are capable of being modifiedfor her of 56. The adhesive prepared in this manner the type ofproduction schedule desired. in was spread on 5 birch panels in anamount The partially esterified sebacic acid glycerol sufilcient to give8 grams per glue line for 4" x 12" was dissolved in Solox, a denaturedalcohol panels. These panels were laminated into lamicontainingapproximately 87.3% ethanol, to nates of 3 and 6 ply by pressing at 250p. s. i. make a 50% solution. The sebacic acid glycerol pressure andusing radio frequency heat, 3.4 kiloand "Solox is preferably reacted todecrease the 55 watt at 10 megacycles input, the voltage at the acidnumber of the solution. With the exception electrode being 1.5kilovolts. The following table of stability of product. the acid numberis not summarizes the results obtained from this com- -of criticalimportance. However, from the standposition.

Dry Soak 48 Hours Boil 3 Hrs. 43 am u 1 on n Percent Percent PercentMinutes .lbs w lbs. w lbs. w Break Fai re Break Fai iare Break Folia e 2hm set: o 620 100 e10 100 500 100 2 a. it?) *s a a s 1% a 590 10 600 so550 loo 3 hr. Bet:

-i 2 a s as s s2 23 es 100 s40 590 154 3 so?) 40 620 so 620 i% 6 m m: s670 680 100 (no 100 i a; a as is. a :22 34mm a 620 so 650 100 610 100EXAMPLE 5 Plywood laminates were prepared according to the procedure ofExample 4 with the exception that the Solox solution of sebacic acidglycerol was reacted to an acid number of only 194. The followingexamples summarize the results obtained from this adhesive:

sure to radio frequency, the partially esterifled sebacic acid glycerolmelamine formaldehyde adhesive does not overcure, burn or char. This isa favorable factor since it is an additional indication that cure timeis not critical for this composition. This factor is not true in thecase of some other types of adhesives, particularly urea Dry Soak 48Hours Boil 3 Hrs. c diti t i I on 0115 "He 11 Minutes lbs. al" lbs. gggglbs. $533,? Break Failure Break Failure Failure 2 hr. set: 6 71 100 700100 63 100 0 0 2 min. B. F. 3 80 2?? 100 s 90 100 34min. R. F.{ 3 720100 040 100 610 100 3 hr. set: 700 100 590 100 530 100 e 2 min. B. F. 39 100 290 510 100 s 90 100 600 100 114mm. R. F. I 3 560 60 630 10 540 5hr. set: 690 100 no 100 650 100 6 2 min. R. F. 3 $5 3 100 g 1 $3 123 s15mm. R. F. 3 730 100 510 100 540 100 EXAMPLE 6 and urea modifiedadhesives, since their cure time Example 4 was repeated with theexception of the acid number of the sebacic acid glycerol solution beingonly 137 in table summarizes the res adhesive mix prepared in thiscomposition:

this case. The following 30 ults obtained using an using radio frequencyheat is very critical.

EXAMPLE 7 A composition was prepared using a mixed resin prepared asfollows: the melamine formaldehyde Dry Soak 48 Hours Boil 3 Hrs. PressConditions time in Minutes lbs. 8532 5 lbs. m" lbs. gg? Break FailureBreak Failure Break Failure 2 hours. set:

6 780 90 640 100 600 so 3 s a a; a it; e o o 0 h 3 550 so 630 100 580100 3 Lse o 610 100 560 100 550 100 3 a as 1"" a l v e e o 00 00 h 3 660100 630 100 570 100 5 r. set:

2mm. R 6 (so I00 600 100 660 100 3 600 100 630 100 600 100 s 680 100 030100 680 100 193mm 3 040 so 600 100 540 100 In the above Examples 4, 5and 6, edgewise as well as parallel electrodes were set up, andtemperature measurements were made in the laminates to determine thetemperature gradient, if any, between the wood and the glue line. Thefollowin table presents the temperature gradients determined betweenwood and glue line:

Temperature Gluo Run No. Line Wood 203F., 1 ply apart. 127F., 1 inchapart. 215F., 2 min. R. F. 307 258F., 4 mill. R. F? 338 271F., 6 ulin.R. F?

gewl'se electrodes 2 minutes R. F. electrodes at 2.4 kw.

at 1.2 kw.

#1 8nd #2 ed #3 Parallel 1 Thermocouples l-l" apart. I Thermocouples ts"apart.

that temperature for 15 minutes, g sufficient urea to make the ratio offormaldehyde to urea approximately 1.721. The mixture was reheated toreflux and held for the desired viscosity. The blend of these two resinsyrups was spray dried and the powder obtained therefrom blended to givea composition comprisin approximately parts resin, 1'7 parts wood flourand 3 parts tricalcium phosphate. T0 parts of this composition there wasadded 65 parts of water and 2 parts of a 50% Solox" solution ofpartially esterified sebacic acid glycerol. The adhesive of thiscomposition was applied to birch panels which were superimposed upon oneanother to form a laminate which was pressed at 250 p. s. i. in a radiofrequency press. After many experimental tests it was ascertained thatthe radio frequency exposure time is critical and lies between 30 and 45seconds, since panel laminates with exposure time below 30 secondsmately 7.8 by heating to reflux exposure could be delaminated' by hand,and those subjected to an exposure time above 45 seconds arc'ed andcharred. There was further noted that the temperature gradient betweenthe wood and the glue line was relatively small. For example, when theradio frequency time was 30 seconds, the relative temperatures were 190F. wood line. and 197 F. glue line, while at 45 seconds radio frequencyexposure time, the wood line was 240 F. and the glue line was 249 F.

We claim:

1. A thermosetting adhesive suitable for radio frequency gluingcomprising thermosetting melamine-formaldehyde resin and 1% to 5% anester obtained by reacting substantially equal molecular proportions ofglycerol and sebacic acid, said percentage being based on the weight ofthe resin solid.

2. A thermosetting adhesive suitable for radio frequency gluingcomprising melamine-formaldehyde resin and 1% to of an ester obtained byreacting substantially equal molecular proportions of glycerol andsebacic acid, said percent: ages being based on the weight of the resinsolid, dispersed in a volatile liquid media.

. 3. A thermosetting adhesive suitable for radio frequency gluingcomprising an aqueous dispersion of thermosetting melamine-aldehyderesin and 1% to 5% by weight of an ester obtained by reactingsubstantially equal molecular proportions 01' glycerol and sebacic acid,based on the weight of the resin solid.

4. A laminate comprising wooden panels bonded together in superimposedrelationship with an adhesive comprisin thermosettingmelamine-formaldehyde resin and 1% to 5% of an ester obtained byreacting substantially equal molecular proportions of glycerol'andsebacic acid, based on the weight of the resin solid.

5. A thermosetting adhesive suitable for radio frequency gluingcomprising a mixture of an aqueous dispersion of thermosettingmelamineformaldehyde resin and a volatile organic solution of 1% to 5%by weight oi! an ester obtained by reacting substantially equalmolecular proportions of glycerol and sebacic acid. said percentagebeing based on the weight of the resin solid.

JOHN C. MEAD. WILLIAM C. SCHNEIDER.

RIJFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,197,357 Widmer et al Apr.16,1940 2,386,744 Myers Oct. 9, 1945 2,460,186 Moffett Jan. 25, 1949FOREIGN PATENTS Number Country Date 533,997 Great Britain Feb. 25, 1941867,065 France June 30, 1941

1. A THERMOSETTING ADHESIVE SUITABLE FOR RADIO FREQUENCY GLUINGCOMPRISING THERMOSETTING MELAMINE-FORMALDEHYDE RESIN AND 1% TO 5% OF ANESTER OBTAINED BY REACTING SUBSTANTIALLY EQUAL MOLECULAR PROPORTIONS OFGLYCEROL AND SEBACIC ACID, SAID PERCENTAGE BEING BASED ON THE WEIGHT OFTHE RESIN SOLID.